Fabrication of organic and polymer nanocrystals using supercritical fluid

Previously, we reported that nanocrystals of organic and polymeric compounds can easily be obtained by reprecipitation from their solution. The reprecipitation method, however, is not applicable to compounds that are hard to dissolve in conventional solvents. To address this issue, an advanced method, i.e. the supercritical fluid reprecipitation (SCFR) method has been investigated; the nanocrystallization of difficult-to-dissolve compounds such as phthalocyanine and fullerenes has become possible. In the case of titanylphthalocyanine, the γ-form-nanocrystals 50 nm in size could be prepared by using supercritical acetone in SCFR method. The performance of the organic photoconductors was evaluated. When C₆₀ was subjected to this technique, the nanocrystals with size of about 40 nm could be fabricated in the dispersion liquid. The optical properties were found to be dependent on the crystal size in a similar manner to that for other ∏-conjugated organic nanocrystals. The nanocrystallization of polydiacetylene and others were also possible using SCFR method. The results were compared with those obtained by the conventional reprecipitation method.